U.S. patent application number 09/778893 was filed with the patent office on 2001-09-13 for switching device.
Invention is credited to Aendekerk, Everaard Marie Jozef, Van Der Veen, Geert Willem.
Application Number | 20010020831 09/778893 |
Document ID | / |
Family ID | 8170997 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010020831 |
Kind Code |
A1 |
Van Der Veen, Geert Willem ;
et al. |
September 13, 2001 |
Switching device
Abstract
In a ballast circuit for operating a lamp, which comprises a
bridge circuit and a control circuit for controlling the bridge
switches, the control circuit comprises a microprocessor. The
control signal for controlling the switches is generated by a
separate circuit comprising a signal generator, a timer, two
comparators and two reference signal generators. The microprocessor
is used only to set the reference signals to the desired values,
thereby dimming the lamp.
Inventors: |
Van Der Veen, Geert Willem;
(Eindhoven, NL) ; Aendekerk, Everaard Marie Jozef;
(Eindhoven, NL) |
Correspondence
Address: |
Jack E. Haken
U.S. Philips Corporation
580 White Plains Road
Tarrytown
NY
10591
US
|
Family ID: |
8170997 |
Appl. No.: |
09/778893 |
Filed: |
February 7, 2001 |
Current U.S.
Class: |
315/209R ;
315/212; 315/215; 315/217; 315/226 |
Current CPC
Class: |
Y02B 20/186 20130101;
H05B 41/3927 20130101; H05B 41/2828 20130101; Y02B 20/00
20130101 |
Class at
Publication: |
315/209.00R ;
315/212; 315/215; 315/217; 315/226 |
International
Class: |
H05B 037/02; H05B
039/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 10, 2000 |
EP |
00200439.8 |
Claims
1. A switching device for energizing a lamp, comprising input
terminals which are to be connected to the poles of a
supply-voltage source, a DC-AC converter for generating a
high-frequency lamp current of frequency f from a supply voltage
supplied by the supply-voltage source, which DC-AC converter
comprises a branch including a series arrangement of a first and a
second switching element, respective ends of which are coupled to
the input terminals, a control circuit including a microprocessor
for rendering the first and the second switching element
alternately conducting and non-conducting, which control circuit is
provided with a dim circuit having a timer for adjusting a first
time interval, during which the first switching element is
conducting, and for adjusting a second time interval during which
the second switching element is conducting, characterized in that
an input of the timer is connected to a signal generator for
generating a signal whose frequency is higher than the clock rate
of the microprocessor, and in that the timer is provided with a
reset circuit for resetting the timer with a frequency 2*f, and in
that the dim circuit further comprises a first comparator, a first
input of which is coupled to an output of the timer, and a second
input is coupled to an output of a first reference circuit for
generating a signal which is a measure of a desired value of the
first time interval, and an output of which comparator is coupled
to a control electrode of the first switching element, a second
comparator, a first input of which is coupled to the output of the
timer, and a second input is coupled to an output of a second
reference circuit for generating a signal which is a measure of a
desired value of the second time interval, and an output of which
comparator is coupled to a control electrode of the second
switching element.
2. A switching device as claimed in claim 1, wherein an input of
the first reference circuit and an input of the second reference
circuit are coupled to the microprocessor.
3. A switching device as claimed in claim 1 or 2, wherein an input
of the timer is coupled to the output of a reset circuit, and an
input of the reset circuit is coupled to the microprocessor.
4. A switching device as claimed in claim 1, 2 or 3, wherein the
control circuit comprises a coupling-circuit part which is used for
maintaining, during a third time interval having a duration 1/2*f,
an electric connection between the output of the first comparator
and the control electrode of the first switching element, and for
interrupting an electric connection between the output of the
second comparator and the control electrode of the second switching
element, and for maintaining, during a fourth time interval having
a duration 1/2*f, an electric connection between the output of the
second comparator and the control electrode of the second switching
element, and for interrupting an electric connection between the
output of the first comparator and the control electrode of the
first switching element.
5. A switching device as claimed in claim 4, wherein the
coupling-circuit part comprises a bistable multivibrator, an input
of which is coupled to an output of the timer, a first and gate, a
first input of which is coupled to a first output of the bistable
multivibrator, a second input of which is coupled to the output of
the first comparator, and an output of which is coupled to the
control electrode of the first switching element, and a second and
gate, a first input of which is coupled to a second output of the
bistable multivibrator, a second input of which is coupled to the
output of the second comparator, and an output of which is coupled
to the control electrode of the second switching element.
6. A control circuit for use in a switching device as claimed in
any one of the preceding claims.
7. A control circuit as claimed in claim 6, wherein the
microprocessor, the timer, the first reference circuit, the second
reference circuit and the coupling-circuit part are integrated in
an IC.
Description
[0001] The invention relates to a switching device for energizing a
lamp, comprising
[0002] input terminals which are to be connected to the poles of a
supply-voltage source,
[0003] a DC-AC converter for generating a high-frequency lamp
current of frequency f from a supply voltage supplied by the
supply-voltage source, which DC-AC converter comprises
[0004] a branch including a series arrangement of a first and a
second switching element, respective ends of which are coupled to
the input terminals,
[0005] a control circuit including a microprocessor for rendering
the first and the second switching element alternately conducting
and non-conducting, which control circuit is provided with a dim
circuit having
[0006] a timer for adjusting a first time interval, during which
the first switching element is conducting, and for adjusting a
second time interval, during which the second switching element is
conducting.
[0007] The invention also relates to a control circuit for use in
such a switching device.
[0008] A switching device of the type mentioned in the opening
paragraph is known from WO 99/01013. As the control circuit
comprises a microprocessor, many different functions of the
switching device can be implemented in the control circuit, which,
in spite of that, can be embodied so as to be comparatively small.
For example, the known switching device enables the luminous flux
of the lamp to be adjusted at a desired value by influencing the
conduction times of the switching elements. To achieve this,
software is employed enabling a number to be set in the timer by
the microprocessor, the value of said number being a measure of the
desired conduction time of a switching element or a measure of the
desired length of a time interval during which the switching
elements are both non-conducting. Subsequently, the contents of the
timer is reduced to zero by the microprocessor in a number of steps
that is equal to the number set in the timer. When the value of the
number in the timer has been reduced to zero by the software, one
of the switching elements is rendered conducting or non-conducting.
A drawback of this method of dimming a lamp energized by means of
the switching device resides in that the resolution of the time
intervals adjusted by means of the timer is determined by the time
needed by the microprocessor to execute a command originating from
the software. Unless use is made of a very expensive
microprocessor, this means in practice that the resolution is
comparatively poor. As a result, the number of levels of the
luminous flux of the lamp that can be adjusted by means of the
control circuit is comparatively small. A further drawback of the
known switching device resides in that, during stationary
operation, the microprocessor almost continuously determines
conduction times of switching elements and/or time intervals during
which both switching elements are non-conducting. As a result of
this further drawback, the capacitance that remains to execute
other functionalities, such as control functions etc, is very
limited.
[0009] It is an object of the invention to provide a switching
device by means of which the luminous flux of a lamp energized
using the switching device can be adjusted at a comparatively large
number of values, while, apart from controlling the conduction
times of the switching elements, the microprocessor is capable of
carrying out a large number of other functions during stationary
operation.
[0010] To achieve this, a switching device of the type mentioned in
the opening paragraph is characterized in accordance with the
invention in that an input of the timer is connected to a signal
generator for generating a signal whose frequency is higher than
the clock rate of the microprocessor, and in that the timer is
provided with a reset circuit for resetting the timer with a
frequency 2*f, and in that the dim circuit further comprises a
first comparator, a first input of which is coupled to an output of
the timer, and a second input is coupled to an output of a first
reference circuit for generating a signal which is a measure of a
desired value of the first time interval, and an output of which
comparator is coupled to a control electrode of the first switching
element, a second comparator, a first input of which is coupled to
the output of the timer, and a second input is coupled to an output
of a second reference circuit for generating a signal which is a
measure of a desired value of the second time interval, and an
output of which comparator is coupled to a control electrode of the
second switching element.
[0011] In a switching device in accordance with the invention, the
contents of the timer is changed with the frequency of the signal
generator. This frequency is independent of the clock frequency of
the microprocessor and can be selected so as to be much higher than
said clock frequency. This comparatively high frequency of the
signal from the signal generator results in a comparatively high
resolution of the time intervals determined by means of the timer.
As a result of this high resolution, the luminous flux of the lamp
can be set to a comparatively large number of values.
[0012] In a preferred embodiment of a switching device in
accordance with the invention, an input of the first reference
circuit and an input of the second reference circuit are coupled to
the microprocessor. In this preferred embodiment, the output
signals of the first and the second reference circuit, and hence
the conduction times of the first and the second switching element,
can be adjusted by means of the microprocessor.
[0013] Satisfactory results have also been obtained in examples of
a switching device in accordance with the invention, wherein an
input of the timer is coupled to the output of a reset circuit, and
an input of the reset circuit is coupled to the microprocessor. In
such examples, the reset circuit resets the timer with a frequency
f, which can be set via the microprocessor.
[0014] To preclude that both switching elements become conducting
at the same time, the control circuit of a switching device in
accordance with the invention is preferably provided with a
coupling-circuit part which is used for
[0015] maintaining, during a third time interval having a duration
1/(2*f), an electric connection between the output of the first
comparator and the control electrode of the first switching
element, and for interrupting an electric connection between the
output of the second comparator and the control electrode of the
second switching element, and for
[0016] maintaining, during a fourth time interval having a duration
1/(2*f), an electric connection between the output of the second
comparator and the control electrode of the second switching
element, and for interrupting an electric connection between the
output of the first comparator and the control electrode of the
first switching element. Said first time interval forms part of the
third time interval and said second time interval forms part of the
fourth time interval. In the third time interval, the first
switching element is conducting during a time interval which is
equal to the first time interval. During the remaining part of the
third time interval, the first switching element is non-conducting.
The second switching element is non-conducting during the whole
third time interval. Correspondingly, in the fourth time interval,
the second switching element is conducting during a time interval
which is equal to the second time interval. During the remaining
part of the fourth time interval, the second switching element is
non-conducting. The first switching element is non-conducting
during the whole fourth time interval. In an advantageous
embodiment of such a coupling-circuit part, the coupling-circuit
part comprises
[0017] a bistable multivibrator, an input of which is coupled to an
output of the timer,
[0018] a first and gate, a first input of which is coupled to a
first output of the bistable multivibrator, a second input of which
is coupled to the output of the first comparator, and an output of
which is coupled to the control electrode of the first switching
element, and
[0019] a second and gate, a first input of which is coupled to a
second output of the bistable multivibrator, a second input of
which is coupled to the output of the second comparator, and an
output of which is coupled to the control electrode of the second
switching element.
[0020] In this manner, the coupling-circuit part is formed in a
comparatively simple and reliable manner.
[0021] Preferably, the microprocessor, the timer, the first
reference circuit, the second reference circuit and the
coupling-circuit part of a control circuit of a switching device in
accordance with the invention are integrated in an IC. As a result,
the control circuit, and hence the switching device in accordance
with the invention, can be embodied so as to be comparatively
compact.
[0022] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiment(s) described
hereinafter.
[0023] In the drawings:
[0024] FIG. 1 shows an example of a switching device in accordance
with the invention to which a lamp La is connected, and FIG. 2 is a
more detailed view of the control circuit of the example shown in
FIG. 1.
[0025] In FIG. 1, K5 and K6 are terminals which are to be connected
to the poles of an AC voltage source, such as mains voltage. The
terminals K5 and K6 are connected to respective input terminals of
rectifier means GM for rectifying an AC voltage supplied by the AC
voltage source. A first output terminal of the rectifier means GM
is connected to a second output terminal of the rectifier means GM
by means of a series arrangement of a coil L2 and a switching
element S3. The switching element S3 is shunted by a series
arrangement of diode D1 and capacitor C1. A control electrode of
the switching element S3 is connected to an output of a circuit
part SC2. An input of the circuit part SC2 is connected to a
junction point of diode D1 and capacitor C1. Circuit part SC2 is a
circuit part used for rendering switching element S3 conducting and
non-conducting. Coil L2, diode D1, switching element S3, circuit
part SC2 and capacitor C1 jointly form a DC-DC converter. This
DC-DC converter generates, during operation of the switching
device, a substantially constant DC voltage from the rectified AC
voltage. This substantially constant DC voltage is present across
capacitor C1. The operation and the dimensions of such a DC-DC
converter are known in the art of lighting electronics. The AC
voltage source, the rectifier means GM and the DC-DC converter
jointly form a supply-voltage source. This supply-voltage source
supplies a supply voltage, which is formed by the substantially
constant DC voltage present across capacitor C1. Capacitor C1 is
shunted by a series arrangement of switching elements S1 and S2. In
this example, respective ends of this series arrangement form input
terminals K1 and K2, which are to be connected to a supply-voltage
source. Control electrodes of switching elements S1 and S2 are
connected to respective outputs of circuit part SC1, which in this
example forms a control circuit for rendering the first and the
second switching element alternately conducting and non-conducting.
Circuit part SC1 and switching elements S1 and S2 jointly form a
DC-AC converter for generating a high-frequency lamp current of
frequency f from the supply voltage. Switching element S2 is
shunted by a series arrangement of coil L1, lamp terminal K3,
discharge lamp La, lamp terminal K4 and capacitor C2. Lamp
terminals K3 and K4 are terminals for accommodating a lamp to be
energized by the switching device. Lamp terminals K3 and K4 are
interconnected by means of a capacitor C3. Coil L1, lamp terminals
K3 and K4, lamp La and capacitors C2 and C3 jointly form a load
branch of the DC-AC converter.
[0026] The operation of the example shown in FIG. 1 is as
follows.
[0027] If terminals K5 and K6 are connected to an AC voltage
source, the rectifier means GM rectify the AC voltage supplied by
the AC voltage source, and circuit part SC2 renders the switching
element S3 alternately conducting and non-conducting. In this
manner, the DC-DC converter generates a substantially constant DC
voltage from the rectified AC voltage, which DC voltage is present
across capacitor C1. Circuit part SC1 renders the switching
elements S1 and S2 alternately conducting and non-conducting with a
frequency f. As a result, a substantially square-wave voltage of
frequency f is applied across the load branch. This substantially
square-wave voltage causes a high-frequency current of frequency f
to flow in the load branch, so that a high-frequency current of
frequency f also flows through the lamp La. The control circuit is
provided with a dim circuit for adjusting the luminous flux of the
lamp La. This luminous flux is adjusted by setting a first time
interval during which the first switching element S1 is conducting,
and setting a second time interval during which the second
switching element S2 is conducting. The way in which the first and
the second time interval are set will be elucidated with reference
to FIG. 2.
[0028] In FIG. 2, .mu.P is a microprocessor which forms part of the
control circuit. A first output of microprocessor .mu.P is
connected to an input of circuit part Ref 1. A second output of
microprocessor .mu.P is connected to an input of circuit part Ref2.
Circuit part Ref1 forms a first reference circuit for generating a
signal, which is a measure of a desired value of the first time
interval. Circuit part Ref2 forms a second reference circuit for
generating a signal, which is a measure of a desired value of the
second time interval. An output of circuit part Ref1 is connected
to a first input of comparator COMP1. A second input of comparator
COMP1 is connected to a first output of the timer T. An output of
comparator COMP1 is connected to a first input of AND gate AND1. An
output of AND gate AND1 is connected to a control electrode of
switching element S1. An output of circuit part Ref2 is connected
to a first input of comparator COMP2. A second input of comparator
COMP2 is connected to the first output of the timer T. An output of
comparator COMP2 is connected to a first input of AND gate AND2. An
output of AND gate AND2 is connected to a control electrode of
switching element S2. A first input of timer T is connected to an
output of signal generator OSC for generating a signal having a
higher frequency than the clock rate of microprocessor .mu.P. An
input of bistable multivibrator K is connected to a second output
of timer T. The second output of timer T is also connected to a
first input of reset circuit R for resetting timer T with a
frequency 2*f. A second input of reset circuit R is connected to a
third output of the microprocessor .mu.P for adjusting the
frequency f with the microprocessor .mu.P. An output of the reset
circuit R is connected, for this purpose, to a second input of
timer T. A first output of bistable multivibrator K is connected to
a second input of AND gate AND1. A second output of bistable
multivibrator K is connected to a second input of AND gate AND2.
The bistable multivibrator K and the first and the second AND gate
jointly form, in this example, a coupling-circuit part for
alternately maintaining and interrupting, at(?) a frequency f, the
electric connections between the outputs of the comparators COMP1
and COMP2 and, respectively, the first switching element S1 and the
second switching element S2.
[0029] The operation of the control circuit shown in FIG. 2 is as
follows.
[0030] During operation of the switching device, the signal
generator OSC generates a periodic signal having a comparatively
high frequency. During a reset, the reset circuit R makes the
contents of the timer equal to a predetermined value corresponding
to the frequency 2*f. From this moment, the value of the number in
the timer is equal, at any instant, during a time interval of
1/(2*f) to the predetermined value minus the number of periods of
the periodic signal after the latest timer reset. Reference circuit
Ref1 generates a signal, which is a measure of a desired value of
the first time interval. As long as the contents of the timer is
higher than the signal generated by reference circuit Ref1, the
output of comparator COMP1 is high. As soon as the contents of the
timer becomes equal to the signal generated by reference circuit
Ref1, the output of comparator COMP1 changes from high to low. The
contents of the timer decreases further and the output of
comparator COMP1 remains low until a time interval 1/(2*f) has
elapsed after the latest timer reset. The instant at which the
contents of the timer is zero and a time interval 1/(2*f) has
elapsed since the latest timer reset, the reset circuit R resets
the timer, which means that the contents of the timer is made equal
to the predetermined value. After resetting the timer, the contents
of the timer decreases again, and the output of comparator COMP1 is
high again. Similarly, the output of comparator COMP2 is high at
first during each time interval of 1/(2*f), until the contents of
the timer is equal to the signal generated by the reference circuit
Ref2. After that, the output of comparator COMP2 changes from high
to low. At each timer reset, a pulse is generated on the second
output of the timer and hence on the input of the bistable
multivibrator K. If the first output of the bistable multivibrator
K is high, then the second output is low. After a pulse on the
input of the bistable multivibrator K, the first output changes
from high to low and the second output changes from low to high. A
subsequent pulse causes the first output to change from low to high
and the second output from high to low. As a result, during
successive time intervals of 1/(2*f), the first switching element S
1 and the second switching element S2 are alternately rendered
conducting during, respectively, the time interval wherein the
output of comparator COMP1 is high and the time interval wherein
the output of comparator COMP2 is high. Via the microprocessor
.mu.P, the value of the signal generated by the first reference
circuit and/or the value of the signal generated by the second
reference circuit can be adjusted. These values may be chosen to be
equal or different. If these values are chosen to be different, it
becomes possible to adjust the luminous flux of the lamp at many
different levels. The value of the frequency 2*f can also be
adjusted via the microprocessor .mu.P by adjusting the
predetermined value to which the contents of the timer is made
equal at each reset. Apart from adjusting the value of the
reference signals and the frequency 2*f, the microprocessor .mu.P
plays no part in generating control signals. As a result, the
microprocessor is substantially completely available for fulfilling
other functions of the switching device. As the frequency of the
signal generated by the signal generator OSC is comparatively high,
also the resolution of the conduction times of the switching
elements set by means of the control circuit is high, so that the
luminous flux of the lamp can be adjusted at many different
values.
* * * * *